The project's long term goal is to make progress toward the day when open-loop insulin delivery devices can be linked to, and driven by, continuous glucose monitoring. Developing this "closed loop" system, though, requires a reliable, accurate and rapid sensor of blood glucose. The present work involves evaluating the characteristics and accuracy of the glucose sensor arm, a subcutaneously placed continuous glucose monitor. With NIH RO1 support, we are pursuing the fine points of the monitor's response, such as the characteristics of subcutaneous glucose concentration's kinetics (lag times) relative to blood glucose. This information will inform us about the feasibility of driving insulin delivery with the measured glucose.